Short perceptual range and yet successful invasion of a fragmented landscape: the case of the red-bellied tree squirrel (Callosciurus erythraeus) in Argentina

Abstract

Dispersal is a key element of the invasion process for introduced species, and is influenced by landscape connectivity. The red-bellied squirrel (Callosciurus erythraeus) was introduced to Argentina in 1970. Suitable forest habitat for this arboreal species is highly fragmented in a rural–urban matrix, but despite this, the squirrel population has spread. Squirrels disperse into new habitat patches using connective features such as forest corridors. They may also cross gaps but up to what extent is not known. Gap crossing success is influenced by perceptual range, which is the distance from which animals can perceive suitable habitat. Perceptual range has been previously estimated for vulnerable species, but not for introduced species. We used a model relating perceptual range to body mass to predict the perceptual range of the red-bellied tree squirrel in Argentina. We then tested our prediction of 202–221 m by releasing squirrels in an unfamiliar arable field at different distances (300, 200, 100 and 20 m) from woodland habitat. We assumed that if woodland could be perceived, squirrels would orientate toward it. We estimated perceptual range to be between 20 and 100 m, considerably lower than predicted. Our results indicate that squirrels can potentially cross small habitat gaps, but dispersal over greater distances lacking connectivity is less likely. Incorporating this information when modelling the spread of exotic squirrels in the Pampas Region can yield more accurate prediction of the invasion process and guide management practices to minimise their expansion.